It is frequently desirable to restrict the use of telephones, for example so as to avoid unauthorized toll charges. Apparatus for giving effect to this aim is known. Such apparatus in one form thereof includes counting means for counting the number of dial pulls. When these exceed a certain number, generally seven, simple logic means provides an output signal which serves to actuate line disconnect means. In another form of the apparatus, counting means is provided to count one or more dialed digits. Logic means is provided giving an output signal which serves to actuate line disconnect means when a dialed pulse or pulses correspond to predetermined prohibited numbers. Generally in this apparatus the prohibited numbers will comprise the numbers 0 or 1 as the first dialed digit, and 1 as the second dialed digit; the third digit may also comprise a prohibited number. In a variation of this form of apparatus, logic circuitry is programmed to accept specific numbers, generally three digit numbers indicative of local exchanges, and deny all others. Each of the above described forms of the apparatus may be considered to comprise input circuitry for receiving signals representing dialed digits, detection circuitry to recognize prohibited digits, and blocking circuitry responsive to the detection circuitry to restrict the communication.
In many commercial organizations where it is desirable to use a restriction system it may be desirable or even necessary to overcome or disable the system so that selected personnel are able to have complete and unrestricted access to any exchange and number they require. This has been recognized in the past. U.S. Pat. No. 3,873,781--NISSIM, dated Mar. 25, 1975 describes an arrangement where the hand set remains in the cradle while an "access" code is dialed to overcome the restriction. This required a special dial mechanism or switching mechanism at the telephone set. A somewhat similar solution is described in U.S. Pat. No. 4,099,033--MURRAY, dated July 4, 1978 where unauthorized use of a telephone is ensured by a restrictive system where authorized users are provided with a code to be dialed in on a special telephone set or on separate equipment attached to the telephone set. Again, there must be special equipment at the set. Other ways of providing access of unlimited dialing privileges (i.e. unrestricted calling privileges) to authorized users are by means of a coded card inserted into an accessory at the telephone set as described in U.S. Pat. No. 4,045,619--HARRINGTON, dated Aug. 30, 1977, and by means of a precise tone generator applied to the telephone mouth piece as described in U.S. Pat. No. 4,096,357--MOGTADER, dated June 20, 1978. All these require modified or auxiliary equipment at the telephone set.
In my co-pending application Ser. No. 136,735, filed Apr. 2, 1980, now U.S. Pat. No. 4,314,108, commonly assigned herewith, I describe a telephone call restrictor including means for overcoming or disabling the restrictor in response to an access code being dialed using a standard hand set. Briefly, in such system, the hand set is unhooked to seize a central office line, and a programmable code is dialed so as to disable the restrictor. It will be appreciated that in operation the dialed in code will have been received by the central office and acted upon there, and that such signal must be cleared from the central office before dialing the desired telephone number. Clearing is most easily effected by rehooking the phone to release the central office line. My aforesaid toll restrictor includes circuitry for retaining the restrictor in a disabled condition for a short period within which the central office signal may be cleared and the desired telephone number dialed in. Such mode of operation is suitable for key set operation wherein a telephone set is associated with a specific trunk line. In a PABX (Private Automatic Branch Exchange) system, several lines connect between the central office and the PABX. A toll restrictor would normally locate on the central office side of the PABX, and would only be engaged by seizing a central office line, normally by dialing 9. Assuming a line to be seized and an access code to have been dialed in so as to disable the toll restrictor, when the signal is cleared from the central office by hooking the telephone, the seized line and its associated, now disabled, toll restrictor is released. A new line must be seized by dialing 9; however, the PABX will normally allocate lines on a next available line basis, hence it is probable that the newly allocated line will not be that which was earlier engaged. Not only is the user's attempt to dial out frustrated, but one outgoing line remains open for a short period for uncontrolled use.
It is therefore an object of this invention to provide a telephone restriction apparatus suitable for use in a PABX system having means for overcoming or disabling the restriction in response to an access code being dialed.
It is another object of the invention to provide a restriction apparatus as aforesaid which can be disabled by a number code dialed from an unaltered or standard telephone set.
It is yet another object of the invention to provide a telephone restriction apparatus which in one condition will restrict one type of call whilst permitting other types and in another condition will permit all types subject to the access code being dialed, and which may be conditioned using a standard telephone set.